In the last years, external and implantable ventricular assist devices have been increasingly used as a bridging up to the transplantation of a donor heart. The experience gained with these ventricular assist devices have caused new considerations to that extent that these ventricular assist devices should not only be used for bridging up to the transplantation of a donor heart, but also as a long-term measure. Several aspects speak for this. The organs available for a transplantation are rare. The use of an artificial assist devices can stabilise and improve the condition of the patient so that the preconditions for such a transplantation will be more favourable. The main problem of the transplantation of donor organs, namely the repulsion reaction does not occur with artificial supportive systems. An artificial assist device can possibly also result in a recuperation of the damaged heart so that the patient can continue to live with his native heart.
Different supportive systems are tested and used. In general, they only differ in the type of drive.
Electromagnetic systems consist of an electromagnet squeezing out a blood pouch in order to supply the blood. Such an arrangement has been described in detail in the U.S. Pat. No. 3,874,002. Using an electrical motor, electromechanical systems generate a rotation movement which is transformed into a pump movement. Furthermore, electrohydraulic and electropneumatic systems are known in which a liquid or a gas are pumped into a chamber using a hydraulic pump or a compressor in order to move a flexible membrane for the blood supply.
An attempt was made to develop ferrofluid-driven systems as it is known from the above-mentioned U.S. Pat. No. 4,650,485. Using this known blood pump, the membrane of the blood chamber shall directly be moved by a magnetofluid which is excited by a magnetic field to do so. Unfortunately, such an arrangement will not be able to generate the pump pressure required for its purpose of application if the exciter coil systems are not chosen big enough. Therefore this blood pump is not suitable for implantation.
Magnetofluids are stable dispersions with supermagnetic properties. They consist of single domain particles which are available in a homogenous distribution in selectable solvents by means of surface-active substances. The homogenous distribution is also kept in the strong magnetic field (gradient). The DD-Description of the Invention 160 532 describes such a magnetofluid in detail. Magnetofluids with initial permeabilities up to 4 and saturation magnetisations up to 100 mT are known and have been described.
Because of their simple structure and the sturdiness connected with it, mainly electromagnetic drives have gained acceptance.
With regard to the known systems of this kind, there is a high discrepancy between the design and the size on the one hand and the efficiency with the expenditures for energy supply linked with it on the other. Apart from acoustical disturbances, these are factors which demonstrate essential loads for the patient who is stressed anyway.
The invention is based on the task to create a drive for a blood pump for supporting or partially to totally replacing the heart whereby the blood pump in its weight as well as its energy density nearly corresponds to the natural heart and is especially suitable for an implantation whereby a reduction of the total system in comparison with known systems is made possible and the efficiency is improved at the same time.
This task is solved by the blood pump having a ferrofluid-supported electromagnetic drive consisting of one or several electromagnets and force-transforming facilities and with the space of at least one electromagnetic circuit being completely or partially filled with magnetofluid, whereby the poles show permanent-magnetic properties. Thereby, a magnetofluid with a saturation magnetisation of 150 to 450 mT has been used with an initial permeability of 5 to 25, consisting of single domain particles from iron, cobalt or iron/cobalt alloys, a liquid carrier and surface-active substances which effect the colloidal stability of the single domain particles.
The main idea of the invention is that the effect of the space is increased by the applied ferrofluid (ferrofluid, magnet liquid) because of its higher permeability.
This is succeeded because the transition from the highly permeable back-circuit to the fluid results in an increase of the force (Maxwell stress). Moreover, the underpressure of the magnetofluid can be used under certain circumstances. This underpressure is caused that force densities which are directed out from the magnetofluid occur at its free surface (for example to air) under the effect of a magnetic field.
At last, lower excitations are sufficient for the generation of the required pump pressure. This permits a reduction of the drive size and decreases the losses. This improvement is directly linked with the size of the initial permeability and the saturation magnetisation. Due to the magnetofluid, the mechanical impact at the end of the attraction process is also lowered between the poles.
The drive can be directly put on a blood pump in its simplest design as a one-chamber system. In more complicated designs, a two-chamber or four-chamber system is also possible. Thereby, designs in series as well as parallel arrangements are possible as well.
Therefore, the drive can be used in simple coronary circulation supportive systems or can be applied as a partial or even total replacement of the heart in a simulation of the heart function that is as lifelike as possible.
In the following, the invention is described in detail by means of an embodiment which is designed as a one-stage operation shown in the drawing .